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2 votes
Solve 2cos^2x + cosx − 1 = 0 for x over the interval [0, 2 π ).

a.π and π/3
b.π, π/3, and 5π/3
c.1 and 2π/3
d.1, 2π/3, and 4π/3
e.1, π/3, and 5π/3

2 Answers

6 votes

Answer:

Option B is correct for plato

Explanation:


\pi ,(\pi )/(3), and (5\pi )/(3)

User NFC Guy
by
7.7k points
6 votes
Let cos x = a, then
2a^2 + a - 1 = 0,
solving the quadratic equation, we have:
a = 0.5 or -1.

i.e. cos x = 0.5 or cos x = -1
for cos x = 0.5,
x = pi/3, 2pi - pi/3 = pi/3, 5pi/3

for cos x = -1,
x = pi

therefore, x = pi, pi/3, 5pi/3
Answer: B